Transcript net324d-ch4-p1-p2

Voice Performance Measurement
and related technologies
1
PART1: IP SLA
outline
2
 IP SLA principles
 IP SLA components
 Highlighted features of IP SLA
 IP SLA performance metrics
 IP SLA operations
What is IP SLA
3
 Cisco IP SLA is an embedded feature set in Cisco IOS
Software that allows you to analyze service levels for
IP applications and services
The basic principle of IP SLA
4
 An active measurement that uses injected test
packets (synthetic traffic) marked with a time stamp
to calculate performance metrics.
IP SLA measurements benefits
5
 The results allow indirect assessment of the network,
such as Service-Level Agreements (SLA) and QoS
class definitions.
IP SLA components
6
IP SLA consists of two components, both
implemented in Cisco devices:
• Mandatory source device, which generates, receives,
and analyzes the traffic.
• The IP SLA Responder, which is optionally used to
increase accuracy and measurement details.
7
Using time stamps
8
By adding time stamps to the measurement packets at
the destination device, the IP SLA Responder allows
the elimination of the measurement packet
processing time on the destination device. The IP
SLA Responder listens on any standard or userdefined port for UDP, TCP, and Frame Relay packets
generated by the IP SLA source.
9
10
RTT= T4-T1
Latency (one way)=T2-T1
Where :
 T4 is the time stamp at the source after receiving
the traffic
 T1 is the time stamp at the source when
generating traffic
 T2 is the time stamp at the target when receiving
traffic
IP SLA scope
11
 IP SLA is an example of a device instrumentation
technique that does not overlap between accounting
and performance, because it is dedicated to
performance measurement
12
 IP SLA is applicable to both service providers and
enterprises for performance management.
Highlighted features of IP SLA
13
 Network performance monitoring
 SLA monitoring
 IP service network health assessment
 Edge-to-edge network availability monitoring
 Voice over IP (VoIP) performance monitoring
 Application-aware monitoring
 Accuracy
 Flexible operations
 Pervasiveness
 Troubleshooting of network operation
Network performance monitoring
14
 Network performance monitoring— Measures delay,
jitter, packet loss, packet ordering, and packet
corruption in the network.
SLA monitoring
15
 SLA monitoring— Provides service-level monitoring
and verification
IP service network health assessment
16
 IP service network health assessment— Verifies that
the existing QoS settings are sufficient for new IP
services.
Edge-to-edge network availability monitoring
17
 Edge-to-edge network availability monitoring—
Provides proactive verification and connectivity
testing of network resources (for example, indicates
the network availability of a web server).
Voice over IP (VoIP) performance monitoring
18
 Voice over IP (VoIP) performance monitoring—
Analyzes critical parameters for a VoIP deployment,
which are not only jitter and packet loss, but also the
Mean Opinion Score (MOS) and
Impairment/Calculated Planning Impairment Factor
(ICPIF) values. The ICPIF value represents
predefined combinations of loss and delay.
Application-aware monitoring
19
 Application-aware monitoring— IP SLA can emulate
traffic up to the application level—for example, DNS,
DHCP, and web server requests—and can measure
the related performance statistics.
Accuracy
20
 Accuracy— Microsecond granularity for jitter delay
measurements offers the required precision for
business-critical applications.
Flexible operations
21
 Flexible operations— Offer various kinds of
scheduling, alerting, and triggered measurements
Pervasiveness
22
 Pervasiveness— IP SLA is implemented in Cisco
networking devices ranging from low-end to highend
routers and switches. This avoids the deployment
and management of dedicated measurement boxes.
Troubleshooting of network operation
23
 Troubleshooting of network operation— Provides
consistent, reliable measurement that proactively
identifies performance and connectivity problems.
IP SLA collects the following performance
metrics:
24
• Delay (both round-trip and one-way)
• Jitter (one-way)
• Packet loss (one-way)
• Packet sequencing (packet ordering)
• Packet corruption detection
• Path (per hop)
• Connectivity (one-way)
• FTP server or HTTP website download time
• Voice quality scores (MOS, ICPIF)
The various IP SLA operations can be classified
as follows:
25
• ICMP-based operations for Echo, Path Echo, and
Path Jitter.
• UDP-based operations, such as echo, jitter, DNS, and
DHCP.
• TCP-based operations, such as TCP Connect, FTP,
HTTP.
• Layer 2 operations, such as Frame Relay, ATM, and
MPLS.
• VoIP-related operations, such as VoIP Jitter
Abbreviations
26
Meaning
IOS
Internetwork Operating System
ICPIF
Impairment/Calculated Planning Impairment Factor
ICMP
Internet Control Message Protocol
MPLS
Multiprotocol Label Switching
ATM
Asynchronous Transfer Mode
Voice Performance Measurement
and related technologies
27
PART2: VOIP AND CRITICAL PARAMETERS
FOR A VOIP DEPLOYMENT
Outline
28
 VoIP
 Mean Opinion Scores (MOS)
 Impairment/Calculated Planning Impairment Factor
(ICPIF)
 Network Elements in the Voice Path
 Passive Voice Performance Measurement
 Active Voice Performance Measurement
 Cisco CallManager (CCM)
 Calculating voice jitter
VoIP
29
 Voice over Internet Protocol (VoIP), is a technology
that allows you to make voice calls using a
broadband Internet connection instead of a regular
(or analog) phone line.
https://www.fcc.gov/encyclopedia/voice-overinternet-protocol-voip
VoIP
30
 Some VoIP services may only allow you to call other
people using the same service, but others may allow
you to call anyone who has a telephone number including local, long distance, mobile, and
international numbers..
VoIP
31
 Also, while some VoIP services only work over your
computer or a special VoIP phone, other services
allow you to use a traditional phone connected to a
VoIP adapter
VoIP connection
32
 VoIP connects:
 Phone
to Phone
 Computer to Computer
 Phone to computer
33
http://www.ontelecomuk.com/voip.html
VoIP transport protocol
34
VoIP uses RTP (real-time transport protocol) which
runs on top of the User Datagram Protocol (UDP)
Because VoIP does not require reliability.
So the transmitted packet may suffer from different
Impairment such as:



Delay
Jitter
Packet lost
Mean Opinion Scores (MOS)
35
 The dilemma of measuring the quality of transmitted
speech is that it is subjective to the listener. In
addition, each VoIP transmission codec delivers a
different level of quality. A common benchmark to
determine voice quality is MOS.
36
 With MOS, a wide range of listeners have judged the
quality of voice samples on a scale of 1 (bad quality)
to 5 (excellent quality).
Score
Quality
5
Excellent
4
Good
3
Fair
2
Poor
1
Bad
Description of Quality
Impairment
Imperceptible
Just perceptible, but not
annoying
Perceptible and slightly
annoying
Annoying but not objectionable
Very annoying and
objectionable
MOS-CQE
37
 As the MOS ratings for codecs and other
transmission impairments are known, an estimated
MOS can be computed and displayed based on
measured impairments. The ITU-T calls this
estimated value Mean Opinion Score–
Conversational Quality, Estimated (MOS-CQE) to
distinguish it from subjective MOS values.
Calculating MOS
38
 Originally, the MOS was meant to represent the
arithmetic mean average of all the individual quality
assessments given by people who listened to a test
phone call and ranked the quality of that cal
Calculating MOS artificially
39
 Today, human participation is no longer required to
determine the quality of the audio stream. Modern
VoIP quality assessment tools employ artificial
software models to calculate the MOS.
MOS limitation
40
 The MOS is highly subjective. One should not make
decisions on a VoIP system based on the MOS alone.
Other measurable parameters should be analyzed
such as network delay, packet loss, jitter, and so on.
As an alternative to the MOS, a different, less
subjective rating has been introduced
R-Factor
41
 R-Factor is an alternative method of assessing call
quality. Scaling from 0 to 120 as opposed to the
limited scale of 1 to 5 makes R-Factor a somewhat
more precise tool for measuring voice quality.
http://www.tamos.com/htmlhelp/voip -analysis/mosandr_factor.htm
R-Factor
42
 R-Factor is calculated by evaluating user perceptions
as well as the objective factors that affect the overall
quality of a VoIP system, accounting for the Network
R-factor and the User R-factor separately.
http://www.tamos.com/htmlhelp/voip -analysis/mosandr_factor.htm
R-Factor
43
 The following table demonstrates the effect of the
MOS and R-Factor on the perceived call quality.
http://www.tamos.com/htmlhelp/voip -analysis/mosandr_factor.htm
R-Factor
44
 Some users believe R-Factor to be a more objective
measure of the quality of a VoIP system than MOS.
Still, a network analyzer should be able to calculate
both scores and produce the two assessments for
better judgment of the call quality.
http://www.tamos.com/htmlhelp/voip -analysis/mosandr_factor.htm
Impairment/Calculated Planning Impairment
Factor (ICPIF)
45
 ICPIF attempts to quantify the impairments to voice
quality that are encountered in the network.
Impairment/Calculated Planning Impairment
Factor (ICPIF)
46
ICPIF is calculated by the following formula:
ICPIF = Io + Iq + Idte + Idd + Ie – A
where:
• Io— Impairment caused by nonoptimal loudness rating
• Iq— PCM quantizing distortion impairment
• Idte— Talker echo impairment
• Idd— One-way delay impairment
• Ie— Equipment impairment
• A— An Advantage or expectation factor that compensates
for the fact that users may accept quality degradation,
such as with mobile services
(ICPIF)
47
Upper Limit for ICPIF
Speech Communication Quality
5
Very good
10
Good
20
Adequate
30
Limiting case
45
Exceptional limiting case
55
Customers likely to react strongly
(complaints, change of network
operator)
Network Elements in the Voice
Path
48
Passive Voice Performance
Measurement
Active Voice Performance
Measurement
Passive Voice Performance Measurement
49
 Cisco voice gateways calculate the ICPIF factor
 If this value exceeds a predefined ICPIF threshold,
an SNMP notification is generated.
 The call durations must be at least 10 seconds for the
gateway to calculate the ICPIF value for the call.
Active Voice Performance Measurement
50
 Cisco IOS IP SLA uses synthetic traffic to measure
performance between multiple network locations or
across multiple network paths.
 It simulates VoIP codecs and collects network
performance information, including response time,
one-way latency, jitter, packet loss, and voice quality
scoring.
Cisco CallManager (CCM)
51
http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-managercallmanager/30266-ts-ccm-301.html
Cisco CallManager (CCM)
52
 Cisco CallManager is an IP-based PBX that controls
the call processing of a VoIP network. CCM is a
central component in a Cisco Communication
Network (CCN) system
53
CCM distribution
54
 A CCN comprises multiple regions, with each region
consisting of several CallManager groups with
multiple CallManagers.
CCM main function
55
 CCM establishes voice calls and gathers call detail
information in a VoIP environment. It generates
records for each call placed to and from IP phones,
conferences bridges, and PSTN gateways.
56
http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-managercallmanager/30266-ts-ccm-301.html
Call records types
57
Two different types of call records are produced:
 Call Detail Records (CDR)
 Call Management Records (CMR)
CDR
58
 Call Detail Records (CDR) store call connection
information, such as the called number, the date and
time the call was initiated, the time it connected, and
the termination time. In addition, CDRs include call
control and routing information.
CMR
59
 Call Management Records (CMR) store information
about the call's audio quality, such as bytes and
packets sent or dropped, jitter, and latency. CMRs
are also called diagnostic records.
Generating CDR
60
CCM generates a CDR when:
 A call is initiated or terminated or
 If significant changes occur to an active call, such as
transferring, redirecting, splitting, or joining a call.
Generating CMR
61
 When diagnostics are enabled at the CCM, a CMR is
stored for each call, separately for each IP phone
involved or each MGCP gateway
Discovering voice quality
62
 Voice quality trends can be discovered by inspecting
the CDR's corresponding CMRs. The two records are
linked by the GlobalCallID_callManagerId and
GlobalCallID_Called fields in the CDR and CMR
63
http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-managercallmanager/30266-ts-ccm-301.html
Calculating voice jitter
64
Calculating voice jitter
65
 To measure Jitter, we take the difference between
samples, then divide by the number of samples
(minus 1).
Jitter=difference between samples/(the number of samples-1)
Example
66
 Here's an example. We have collected 5 samples with
the following latencies: 136, 184, 115, 148, 125 (in
that order). The average latency is 142 - (add them,
divide by 5). The 'Jitter' is calculated by taking the
difference between samples.
136 to 184, diff = 48
184 to 115, diff = 69
115 to 148, diff = 33
148 to 125, diff = 23 (Notice how we have only 4 differences for 5
samples). The total difference is 173 - so the jitter is 173 / 4, or
43.25.
Abbreviations
67
Meaning
MOS-CQE
Mean Opinion Score–Conversational Quality, Estimated
RTP
real-time transport protocol
CCN
Cisco Communication Network
CCM
Cisco CallManager
CDR
Call Detail Records
CMR
Call Management Records
PSTN
public switched telephone network
PBX
private branch exchange